It is increasingly known to use the braking energy in motor vehicles by employing, varying or increasing a generator torque of an electric machine.
German Application No. DE 10 2004 051530 A1 describes a motor vehicle which includes a generator and a capacitor. During coasting of the motor vehicle, recuperative energy is generated by the generator as the recuperator and stored in the capacitor. To avoid excessively rapid deceleration of the vehicle in recuperation mode, which is felt to be unpleasant, the generator power is varied by an exciting current in the excitation circuit of the generator as a function of at least one vehicle-specific operating parameter and/or the instantaneous state of charge of the capacitor.
German Application No. DE 10 2007 036 402 A1 describes a method for operating an electric machine in a vehicle, the electric machine being regulated as a function of calculated, driving condition-related measured variables as a function of a driving dynamics limit range when the vehicle is in such a range, for the purpose of reducing or increasing a torque of the electric machine which functions as a generator, for stabilizing the vehicle.
German Application No. DE 10 2008 061 821 A1 describes a method for recuperating energy in a motor vehicle during a recuperative operating state in which free energy is converted into electrical power and stored in the vehicle electrical system or made available directly to a vehicle power unit, the vehicle being in the recuperative operating mode during a coasting phase and/or a braking phase. To recover a much larger amount of energy, energy recuperation is carried out without actuating the brake pedal or without active brake intervention when a driver-side or system-side deceleration request is detected resulting in a higher recuperative power compared to the recuperative power during coasting.